I have a function ( y = f(x) ) that I want to graph in Excel in an xy scatter plot. I usually just make a column of x values and then a column for the y values as a function of the first column, then make the plot based on this set of about 20 points. Is there any way to make a plot straight from the equation, like you would in a graphing calculator?

I hope I'm making myself clear, but if not, let me know and I'll try to elaborate. The function isn't of the type that can have a trend line or polynomial fit, so I can't just do the regression and use that as the function.

I guess I might as well put the equation I'm using:

y = a*x/(1+(a-1)*x) where 'a' is a known constant

BigPete

02-18-03, 10:51 PM

In short, no ... not to my knowledge. Your only hope would be to generate a crapload of points and the try to get excel to apply the right trendline to it so it would return the original equation. I don't think it can create something in that form, though. :(

sdcrym

02-18-03, 10:53 PM

That's what I figured, but thanks anyway. I was just curious :)

BigPete

02-18-03, 10:58 PM

Originally posted by sdcrym
That's what I figured, but thanks anyway. I was just curious :)

Yeah, I guess I didn't really bother to read past your first sentence or I would have known you knew all that and I could have just said 'no' ... oops. :D

tanman

02-19-03, 12:26 AM

Actually I really need help too and was about to start my own thread. I need to make a graph using specific plot points (x,y) and need to find the linear equation of the best fit line y=mx+b how do I do that?

Its for chemistry. I'm plotting a standard curve for a Bradford and BCA assay in order to find the concentration for an unknown sample. If you were curious.

sdcrym

02-19-03, 01:44 AM

Well, my response to you depends on how much you know about Excel already. In short, highlight the x and y columns in a spreadsheet, click the make chart button, select xy scatter. Make sure the next page has the x's and y's in the right place. I'm leaving out a lot of details, but you should be able to figure it out. After the scatter plot is displayed, right click on a data point and select add trendline. Make sure linear is selected, then move over to the options tab and check the display equation box.

Sorry for the incoherence... I just finished up my homework and now I'm off to bed :)

tanman

02-19-03, 08:29 PM

Thank you very much! your help is much appreciated. I could figure it out.